Beam correcting device for mass spectrometers and method of operation

ABSTRACT

A beam correcting device which may be utilized with mass spectrometers for altering the configuration of the beam of ions passing through the mass spectrometer. The beam altering device may include at least four electrodes disposed at substantially equal positions around the beam of ions and positioned at substantially a point along the beam at which the beam is of a minimum thickness. An electrical control circuit is coupled to the electrodes for applying at least four electrical signals, each of a predetermined value, to the electrodes to establish an electrostatic field about the beam of ions. By varying the potentials applied to the various electrodes, a beam having an arcuate cross-sectional configuration may be altered to produce a beam having a generally rectangular cross-sectional configuration thereby compensating for the effect on the beam caused by undesirable fringing fields.

United States Patent Evans et al.

[151 3,657,531 [451 Apr. 17,1972

[54] BEAM CORRECTING DEVICE FOR MASS SPECTROMETERS AND METHOD OF OPERATION [72] Inventors: Sydney Evans, Sale; Reginald Graham,

Wilmslow, both of England [73] Assignee: Associated Electrical Industries Limited,

London, England [22] Filed: May 15, I970 [21] Appl. No.: 39,240

[30] Foreign Application Priority Data May 16, 1969 Great Britain ..25,l09/69 [52] U.S. Cl. ..250/413 ME, 250/419 D [51] Int. Cl. ..l-I0lj 39/34 [58] Field of Search ..-.250/4l.9 D, 41.9 ME

[56] References Cited UNITED STATES PATENTS 3,122,631 2/1964 Geerk et al. ..250/4l.9

OTHER PUBLICATIONS Magnetic Hyperfine Interaction of Cr," By W. J. Childs et al. from Physical Review, Vol. 132, No. 5, Dec. 1, I964, pgs. 2128- 2135 70 VOL T/IGE SUP/ L Y 5 OURCE READ-OUT DE V/CE AMPL lFlfR Primary Examiner-William F. Lindquist Attorney-Watts, Hoffmann, Fisher & l-leinke 57 ABSTRACT A beam correcting device which may be utilized with mass spectrometers for altering the configuration of the beam of ions passing through the mass spectrometer. The beam altering device may include at least four electrodes disposed at substantially equal positions around the beam of ions and positioned at substantially a point along the beam at which the beam is of a minimum thickness. An electrical control circuit is coupled to the electrodes for applying at least four electrical signals, each of a predetermined value, to the electrodes to establish an electrostatic field about the beam of ions. By varying the potentials applied to the various electrodes, a beam having an arcuate cross-sectional configuration may be altered to produce a beam having a generally rectangular crosssectional configuration thereby compensating for the effect on the beam caused by undesirable fringing fields.

ll) Claims, 9 Drawing Figures Fin. l

PATENTED R 18 m2 3, 657, 531 SHEET 2 UF 4 Fifi.5 Fin. 6

INVENTOR. SYD/VE Y E VANS BY REG/NALD GRA HAM WWM%M%M@ ATTORNEYS PATENTEDAPR 18 m2 3, 657, 531 SHEET u UP a REFERENCE SUPPLY SOURCE -94 S +/5 1/ I 2/8- SUM/WING C/ACU/TS 200 W490 334, 5 H8, H0, I42

\y m I 'INVENTOR. S YDNEV EVA/V5 BY REG/NAAD GRAHAM ATTORNE Y5 BEAM CORRECTING DEVICE FOR MASS SPECTROMETERS AND METHOD OF OPERATION BACKGROUND OF THE INVENTION This invention pertains to the art of mass spectrometers, andmore particularly, to a beam correcting system for altering various characteristics of a beam of ions, such as curvature of the cross-sectional configuration of the beam.

Known ion sources have included an ionization chamber into which materials or samples, such as a gas to be analyzed, are introduced in order to ionize the sample by electron bombardment. Generally, the molecules of the gas sample are ionized by an electron beam which passes through the ionization chamber. The ions produced by this ionization process arethen focused and accelerated by a series of electrodes. The ions are then projected through an ion exit slit,or aperture, in the ion source. When such an ion source is employed in a mass spectrometer system, the ions are directed from the exit slit and along an evacuated path to a suitable collecting and/or detecting device. In a single focusing mass spectrometer, the ion path traverses a magnetic analyzer in which the ion beam is subjected to a magnetic deflection by a transverse magnetic field. In a double focusing spectrometer, the ion path traverses an electrostatic analyzer which precedes the magnetic analyzer and subjects the ions to an electrostatic deflection. The analyzers deflect the ions to an extend dependent upon their relative mass numbers. For any given accelerating voltage and magnetic field strength in the analyzer, only ions having a specific mass-charge ratio, or mass number, will pass into the detector. Ions of higher or lower mass numbers will be deflected more or less than the appropriate amount to focus them on the detector.

In these mass spectrometer systems, the magnetic field established by the magnetic analyzer frequently imparts several undesirable characteristics to the beam of ions. Forexample, the fringing fields of the magnetic analyzer frequently produce a curvature of the cross-sectional configuration of the beam thereby increasing the effective width of the beam. This effective width may be reduced somewhat by decreasing the width of the collector slit and collecting only the central portion of the beam. As is apparent, this reduction in the dimensions of the collector slit has the effect of reducing the ion current passing through the collector slit, thereby reducing the overall sensitivity of the spectrometer.

A detailed description of the curvature produced by the fringing fields of a magnetic analyzer is presented in an article entitled, Image Curvature Caused by Fringing Fields in Magnetic Sector Mass Spectrometers" by CliffordE. Berry in the Review of Scientific Instruments, Vol. 27, No. 10, pages 849 through 853, Oct. l956, and incorporated herein by reference.

SUMMARY OF THE INVENTION The present invention is directed toward. a device for altering various characteristics of a beam of ions, thereby over coming the noted disadvantages, and others, of such previous mass spectrometers.

In accordance with one aspect of the present invention there is provided a mass-spectrometer comprising an ionization chamber assemblyforionizing a sample to be analyzed, and an elongated housing member coupled to the ionization chamber and having a passageway extendingtherethrough for the passage of a beam of ions. A magnetic analyzer is positioned to apply a magneticfieldto the beam and a detection device is coupled to the housing member for analyzing the ions passing therethrough. The beam of ions has a cross-sectional configuration which varies in at least one dimension at points along the length of the beam. At one point along the beam this dimension is of a minimum distance. A beam correcting device for altering the cross-sectional configuration of the beam is positioned at substantially the point along the beam of minimum cross-sectionaldimension, and includes each other and to said beam of ions. An electrical circuit is coupled :to each of the electrodes for applying signals, each of a predetermined value, to the electrodes to establish an electrostatic field about the beam of ions to thereby alter the beam at the point of minimum cross-sectionaldirnension.

In accordance with another aspect of the present invention, the beam correcting device includes six electrodes positioned in a generally hexagonalconfiguration about the beam of ions.

In accordancewith still another aspect of the present invention, the beam of ions has at least a second point along its length at which the cross-sectional configuration of the beam has a dimension of a minimum distance, anda second beam correcting device for altering the cross-sectional configuration of the beam is positioned .at substantially the second point. The second beam correcting'device includes a second set of electrodes disposed in spaced relationship with respect to each other and to the ion beam. Also, a second control circuit is coupled to each of the electrodes of the second set of electrodes for applying electrical signals, each of a predetermined value, to the electrodes to establish anelectrostatic field about the beam of ions at the second point of minimum of cross-sectional dimension.

In accordance with still another aspect .of the present invention, the second beam correcting device includes-six elongated pole pieces having longitudinal axes extending in a direction generally parallel to the longitudinal axis of the ion beam and being positioned in a generally hexagonal configuration about the beam.

In accordance with another aspect of the present invention, the mass spectrometer comprises an electrode positioned within the ionization chamber assembly for accelerating ions out of the chamber assembly, and a voltage supply source having an output circuit for developingan accelerating signal and includes a potentiometer for varying the value of the accelerating signal. The output circuit .of the supply source is coupled to the accelerating electrode and is coupled to the ion beamcontrol circuit in a manner so that the value of the elec trostatic field is dependentupon the value .of the signal applied to the accelerating electrode.

In accordance with still another aspect of the present invention, there is provideda method of improving the sensitivity of a mass spectrometer including an ionization chamber assembly having an electrode positioned-within. The chamber assembly is coupled to ,an elongated housing member. The housing member has a through passageway for the passage of a beam of ions. A magnetic analyzer and adetector device are positioned to respectively deflect and detect ions passing through the passageway in:the'housing member. The method includes the steps of introducinga. sample to be analyzed into the ionization chamber assembly, ionizing the sample to thereby form ions, applying an electrical signal to the accelerating electrode to accelerate substantially all of the ions out of the ionization chamber assembly and into the passageway. The method also includes the steps of focusing the ion into a beam, applying an electrical signal to a beam correcting device to thereby develop a field about the beam, altering the cross-sectional configuration of the beam with the field to compensate for the effect on the beam caused by fringing fields of the magneticanalyzer, and applying an electrical signal to the magnetic analyzer to thereby establish a magnetic field about the beam. Then, deflecting with the magnetic field at least a portion of the ions inthe beam so that ions may be analyzed by the detector device.

In accordance with another aspect of the present invention, the method of operating the mass spectrometer also includes the steps of applying an electrical signal to another beam cor recting device to thereby develop a second field about the beam at a second point along the beam, altering the cross-section configuration of thebeam to again compensate for fringing fields of the magnetic analyzer, and collecting at least a portion of the ions with the detector means to thereby analyze the sample.

The primary object of'the present invention is to provide a electrodes disposed in spaced relationship with respect to 5 device for altering the characteristics of a beamof ions.

Another object of the present invention is to provide a beam correcting device which may be utilized with mass spectrometers for eliminating the curvature of a beam caused by the fringing fields established by a magnetic analyzer.

Another object of the present invention is to provide a beam correcting device for rotating a beam of ions about the longitudinal axis of the beam.

Another object of the present invention is to provide a first beam correcting device for mass spectrometers positioned at a point along the beam of ions upstream from a magnetic analyzer for imparting a slight curvature into the cross-section configuration of a beam to form an arcuate-shaped configuration, and a second beam correcting device positioned at a point along the beam downstream from the magnetic analyzer for removing substantially all of the curvature in the cross-sectional configuration of the beam.

Another object of the present invention is to provide a device for altering a beam of ions by moving the beam in a direction perpendicular to a longitudinal axis of the beam, or by varying one or more of the cross-section dimensions of the beam, or by focusing the beam to change the plane of the final image of the beam, or by varying the cross-section configuration of the beam, or by rotating the beam about its longitudinal axis, or by any combination of two or more of these methods.

A further object of the present invention is to provide a mass spectrometer having at least one beam correcting device for compensating for beam curvature which is inherent in substantially every mass spectrometer.

A still further object of the present invention is to provide a device for applying a field to a beam of ions at substantially a point of minimum thickness of the beam in order to compensate for certain undesirable characteristics.

Another object of the present invention is to provide a method of altering the characteristics of a beam of ions in a mass spectrometer in order to improve the resolving power of a mass spectrometer.

A further object of the present invention is to provide a method of altering the characteristics of a beam of ions in a mass spectrometer in order to improve the sensitivity of a mass spectrometer.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and advantages of the invention will become apparent from the following description of a preferred embodiment of the invention, as read in conjunction with the accompanying drawings in which:

FIG. 1 is a sectional view of a typical mass spectrometer including a magnetic analyzer and a pair of beam correcting devices positioned at either end of the analyzer;

FIGS. 2 through 4 are sectional views of a beam of ions taken along planes extending perpendicular to a longitudinal axis of the beam and at various points along the length of the beam;

FIG. 5 is a sectional view of the beam correcting device as illustrated in FIG. 1 taken from a plane extending along the line 5-5 in that figure;

FIG. 6 is a sectional view of the beam correcting device as illustrated in FIG. 5, taken from a plane extending along the line 6-6 of that figure;

FIG. 7 is an electrical circuit diagram of the control circuit for the beam correcting device; and,

FIGS. 8 and 9 are electrical circuit diagrams illustrating in more detail certain of the features of the circuit diagrams of FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, FIG. 1 generally illustrates a double-focusing type mass spectrometer and includes an ionization chamber assembly 10 into which a specimen carrying probe 12 may be inserted. Positioned within the chamber assembly 10 is an electrode 14 to which an accelerating voltage signal is applied, and which serves to repel ions of the samruin ple out of the chamber assembly 10 in the form of a beam of ions 17. The accelerating voltage is developed by voltage supply source S l and is applied through a conductor 15 to the electrode 14. This voltage may be varied in order to vary the acceleration or energy imparted to the ions as the ions are projected out of the chamber assembly 10.

The beam of ions 17 then passes through an electrostatic analyzer 16. The electrostatic analyzer 16 includes a pair of opposed conductive plates 18, 20, between which a potential difference is maintained. The beam of ions 17 then passes through a beam correcting device 22 and into a magnetic analyzer 24.

The magnetic analyzer 24 includes an electromagnetic coil 26 which establishes a magnetic field in a direction transverse to the direction of the beam of ions 17. The ions of the beam, being charged particles, are deflected by the magnetic field. The ions then pass through another beam correcting device 27, and at least a portion of them pass through an adjustable slit 27a positioned in a housing member 28. The ions passing through the adjustable slit 270 then pass into a collector electrode assembly 30 associated with an electron multiplier 32.

Mass spectrometers including an ionization chamber assembly 10, an elongated housing member 34 having an electrostatic analyzer 16, and a magnetic analyzer 24 disposed to deflect ions, are well known in the art. The output signal from the electron multiplier 32 is applied to an amplifier 36, which is in turn coupled to a suitable readout device 38. The collector electrode assembly 30, electrode multiplier 32, amplifier 36, and readout device 38, comprise a detector assembly 39 which is also well known in the art. The detector assembly 39 generally provides a record of the number of ions passing through the adjustable slit 27a in the housing member 28.

The angular deflection of an ion passing through the magnetic analyzer 24 will depend upon the value of the accelerating voltage, since this voltage determines the velocity of the ion. Also, the intensity of the magnetic field in the analyzer 24 affects the angular deflection of the ion. Finally, the mass of the ion passing through the magnetic field is related to the angular deflection of the ion.

FIGS. 2, 3 and 4 illustrate the cross-sectional configuration of the beam of ions 17 at various points along the beam. The coordinate axes X, Y and Z will be used to denote three mutually perpendicular directions with respect to the beam. Accordingly, X denotes the direction parallel to the direction of the ion beam, i.e., in a direction parallel to the longitudinal axis of the beam; Z denotes a direction extending perpendicular to the X direction and generally parallel with the long axis of the cross-section of the ion beam and Y denotes a direction perpendicular to both the X and Z axes.

More particularly, as the ion beam leaves the ionization chamber assembly 10, the cross-sectional configuration of the beam is generally rectangular as shown in FIG. 2. Upon passing through the fringing field of the magnetic analyzer 24, the beam is distorted into a curved, or arcuate, shape as illustrated in FIG. 3. The arcuate shaped beam as shown in FIG. 3 may be restored to the rectangular shape as shown in FIG. 2 by the image correcting devices 22, 27 as will be subsequently described. The ions in the beam have a component of travel in a Z direction and as the ions continue to travel in this direction, the cross-sectional configuration becomes even more distorted to form an even more arcuate shaped configuration as illustrated in FIG. 4.

With this excessive distortion, the top and bottom portions of the cross-sectional configuration are much wider than the central portion. In order to prevent this excessive distortion, it is necessary that the arcuate shaped configuration as illustrated in FIG. 3, be restored to a rectangular configuration within a minimum distance of travel of the beam. FIG. 1 illustrates two image correcting devices 22, 27, which are positioned at both ends of the magnetic analyzer 24. In addition, the beam correcting devices 22, 27 are positioned at substantially the points along the beam of ions 17 where the beam has a minimum cross-sectional width, thereby minimizing unintn'n desirable distortion of the beam by the beam correcting devices 22, 27.

The beam correcting device 22 introduces curvature into the cross-sectional configuration of the beam before the beam enters the magnetic analyzer 24. This induced curvature is in a direction opposite to that normally introduced by the fringing fields of the magnetic analyzer 24, so that as the beam passes through the fringing field at the entrance of the analyzer 24, the curvature is substantially removed. Thus, the cross-sectional configuration of the beam as it passes through the magnetic analyzer 24 has substantially no curvature thereby preventing the beam from traveling for a substantial distance in a curved configuration.

The cross-sectional configuration of the beam is curved again by the fringing fields at the exit of the magnetic analyzer 24. This curvature is then substantially removed by the second beam correcting device 27. Accordingly, the cross-sectional configuration of the beam reaching the slit 27a is of a generally rectangular configuration.

FIGS. 5 and 6 illustrate in more detail the beam correcting devices 22, 27, and generally comprise six elongated cylindrical electrodes 42, 44, 46, 48,50 52, extending generally parallel with respect to each other and positioned at 60 intervals on a circle of a diameter of approximately 1 inch. As illustrated in FIG. 5, the electrodes 42 through 52 form a generally hexagonal configuration when viewed from a plane taken through the electrodes and generally perpendicular to the elongated axes of the electrodes. The electrodes 42 through 52 are approximately one inch in length and of a diameter of approximately one-eighth inch, and each is supported by a pair of ceramic rods of which only the rods 54, 56, 58, 60 are illustrated.

The rods 54, 56, 58, 60 extend into sockets in the end of corresponding electrodes 44, 50, and into corresponding sockets in a pair of generally parallel annular flange members 62, 64. The annular flange members 62, 64 extend inwardly from a support assembly 66.

Six electrical conductors 68, 70, 72, 74, 76, 78 complete an electrical connection to the electrodes 42, 44, 46, 48, 50, 52, respectively. The electrical conductors 68 through 78 are supported by and extend through the support assembly 66 in a glass-to-metal seal arrangement, of which only seals 80, 82 are illustrated.

The annular flange members 62, 64 define a pair of passageways 84, 86, and a pair of tube members 88, 90 are positioned in the passageways 84, 86 respectively. The tube members 88, 90 extend in a direction generally coaxial with a circle formed by the electrodes 42 through 52. The tube members 88, 90, also extend inwardly from the annular flanges 62,

64 to a point inward from the ends of the electrodes 42 through 52, and serve to electrostatically screen the beam of ions to accurately define the limits of the electrostatic field established by the electrodes 42 through 52.

The beam correcting devices 22, 27 are positioned in the elongated housing 34 of the mass spectrometer, so that the beam of ions travels in a direction generally parallel to the electrodes 42 through 52. Thus, when electrical potentials are applied to the electrodes 42 through 52, an electrostatic field is established about the ion beam, and dependent upon the value of the signals applied to the electrodes, various deflections of the beam are possible.

In order to remove the cross-sectional curvature of the ion beam, a positive potential signal is applied to electrodes 44, 48, 52, and an equal negative potential signal is applied to electrodes 42, 46, 50, or vice versa. The electrostatic field established by these signals will exert no net effective force on the ions passing along the axis of the correcting device, however, at points on either side of a plane extending through the electrodes 44, 50, as viewed in FIG. 5, a force is applied to the beam which results in a component force in the Y direction. This force tends to produce curvature of the ion beam. If a beam enters the correcting device having a cross-sectional remove the curvature of the cross-sectional configuration. The magnitude of the electrostatic field may be varied by adjusting the potential applied to the electrodes 42 through 52.

The .beam correcting device may be utilized to rotate the beam of ions 17 about a longitudinal axis of the beam by application of a positive potential signal to electrodes 42, 48, an equal negative potential signal to electrodes 46, 52, or vice versa, and a ground potential signal to electrodes 44, 50.

The beam may be focused in a 2 direction, i.e., a reduction of the dimensions of the beam in the Z direction, by applying a positive or negative potential to electrodes 42, 46, 48, 52, and a ground potential to electrodes 44, 50. As is apparent, other combinations of potentials can be applied to the electrodes to perfonn other operations on the beam, such as Y-focusing, and deflecting the beam in either the Y or Z direction. In addition, these operations may be performed simultaneously by applying to each electrode the sum of the potentials required for the individual operations. Thus, by the operation of the correcting device in a combination of different modes, the beam may be focused, aligned, and curved to be substantially rectangular in cross-sectional configuration.

The required potentials may be applied to each electrode by means of a separate potentiometer; however, it is desirable to provide circuitry for operating the correcting device in various modes by means of a single control.

FIG. 7 illustrates a control circuit for applying the required signals to the electrodes 42 through 52, and generally comprises a voltage supply source S-1 for developing an accelerating voltage signal which is applied through the conductor 15 to the accelerating electrode 14. A signal proportional to the accelerating voltage signal is applied through a potentiometer 92 to a reference source supply circuit 94. The reference source supply circuit 94 develops two signals of equal magnitude but of opposite polarity. These signals are applied through a pair of conductors 96, 98 to opposite ends of each set of a plurality of potentiometers 100, 102, 104, 106, 108, 110, 112, 114, 116, 118.

Each of the sets of potentiometers 100, 102, 104 includes a pair of potentiometers having their sliding contacts ganged in a manner so that the contacts move along the resistive portions in opposite directions. Thus, a pair of output voltages equal in magnitude but of opposite sign are applied to the output terminals 120, 122, and 124, 126 and 128, 130. The potentiometer sets 106 through 118 are comprised of a single potentiometer arranged across the conductors 96, 98, in order to develop voltage signals which are variable between the potential applied to conductor 96 and the potential applied to conductor 98.

The control circuit also includes six identical summing circuits 134, 136, 138, 140, 142, 144, each having five input terminals and an output terminal at which a potential, proportional to the sum of the voltages applied to the input terminals, is developed. The output terminals 146, 148, 150, 152, 154, 156 of the summing circuits 134 through 144, respectively, are connected to the six electrodes 42 through 52, respectively, of the beam correcting device.

The output terminals of the potentiometer sets 100 through 118 are electrically connected to the various input terminals of the summing circuits 134 through 144 as illustrated in FIG. 7. With this circuit arrangement, the potentiometer set 100 may be varied to vary the potential applied to electrodes 42 through 52 in order to effect curvature correction as previously described. The potentiometer sets 102, 104, 106 perform respectively the rotation, Z deflection, and Y focusing operations on the ion beam, as described above. Each of the potentiometers 108 through 118 controls the voltage input to one of the summing units 134 through 144, and therefore varies the potential on the corresponding electrodes 42 through 54. These potentiometers can thus be employed as trimming devices to compensate for any lack of symmetry.

The signal applied to the reference supply source 94 is derived from the voltage supply source 8-1. The supply source curvature, these forces acting in an opposite direction tend to 94 provides the accelerating voltage signal for the electrode 14, therefore, the voltage signals applied to the beam correcting devices 22, 27 are proportional to the accelerating voltage. With this arrangement, the system will automatically adjust to compensate for changes in the accelerating voltage, either due to fluctuations in the voltage supply source S-1, or due to the accelerating voltage being switched between two values when peak matching methods of spectrometer operation are employed. Thus, the control circuit provides a convenient method of applying various corrections to shape the configuration of the ion beam.

FIG. 8 illustrates in more detail the reference supply source 94 and generally comprises a pair of operational amplifiers 160, 162, and associated circuitry for developing a pair of signals equal in value, but opposite in polarity. More particularly, an input signal, proportional to the acceleration voltage signal applied to the conductor 15, is applied to an input terminal 164 of the reference supply source 94. The input terminal 164 is connected through a resistor 166 to the inverting input terminal of amplifier 160. The non-inverting terminal of this amplifier is connected directly to ground and the output terminal of amplifier 160 is connected to the base of a PNP transistor 168. The collector of transistor 168 is connected to a negative lvolt power supply through a resistor 170, and the emitter of this transistor is connected to the inverting input terminal of amplifier 160 through a pair of series-connected resistors 172, 174. The resistors 172, 174 serve as a feedback circuit for the amplifier 160, and resistor 172 is variable so that the value of the feedback signal may be altered. The emitter of transistor 168 also serves as one of the output terminals 96 of the reference supply source 94.

The output signal from terminal 96 is also applied through a restor 17 6 to the inverting input terminal of the amplifier 162. The non-inverting input terminal of amplifier 162 is connected to the base terminal of an NPN transistor 178, and the collector of this transistor is connected through a resistor 180 to a positive l5-volt power supply. The emitter of transistor 178 is connected through a resistor 182 to the inverting input terminal of amplifier 162, and the emitter of this transistor is also connected to the output terminal 98 of the reference supply source 94. Thus, the output voltages developed at terminals 96, 98 are proportional to the accelerating voltage, and may be adjusted to be equal in magnitude to each other by the choosing suitable values for resistors 176 and 182.

FIG. 9 illustrates in more detail the summing circuits 134 through 144 and generally comprises an operational amplifier 186 having its non-inverting input terminal connected to one terminal of five input resistors 188, 190, 192, 194, 196. The other terminals of these resistors 188 through 196 provide five input terminals 198, 200, 202, 204, 206, respectively. The inverting input terminal of amplifier 186 is connected through a resistor 208 to ground, and a series-connected resistor 210 and capacitor 212 are connected in parallel and directly across the resistor 208.

The output terminal of operational amplifier 186 is connected through a resistor 214 to ground, and is also connected to the base of an NPN transistor 216. The collector of transistor 216 is connected through a resistor 218 to a positive l5-volt terminal of a power supply and the emitter of this transistor is connected to one terminal of a lamp 220. The other terminal of lamp 220 is connected directly to a negative l5-volt terminal of a power supply.

The emitter of transistor 216 is also connected through a resistor 224 to the non-inverting terminal of amplifier 186. A series-connected resistor 226 and capacitor 228 are connected in parallel with resistor 224. In addition, the inverting terminal of amplifier 186 is connected through a resistor 230 to a junction point between a resistor 232 and a photo-sensitive resistive element 234. The other terminal of resistor 232 is connected to a positive BOO-volt terminal of a power supply and the other terminal of the photo-sensitive resistive element is connected directly to a negative 300-volt terminal of a power supply. The junction point between resistor 232 and the photo-sensitive resistive element 234 provides the output terminal of the summing circuit and is connected to a corresponding one of the electrodes 42 through 52.

The resistor 230 serves as a feedback path and forces the voltage potential at the junction between resistors 232 and the photosensitive resistive element 234 to be proportional to the sum of all input voltages applied to resistor 230. The lamp 220 is positioned to vary the resistance of the photo-sensitive element 234, so that the signal applied to the output terminal of the summing circuit remains proportional to the sum of the input signals.

Although the invention has been shown in connection with the third embodiment, it will be readily apparent to those skilled in the art that various changes and form of arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention as defined by the appended claims.

Having thus described our invention, we claim:

1. In a mass spectrometer including an ionization chamber for ionizing a sample to be analyzed, said ionization chamber being coupled to an elongated housing member having a through passageway for the passage of a beam of ions, said beam of ions having a cross-sectional configuration which varies in area along the length of said beam and having at least one location at which said area is of a minimum value, a magnetic analyzer disposed to apply to a magnetic field to said beam to analyze said ions, detection means coupled to said housing and disposed to detect said ions after analysis, and beam correcting means for effecting rotation of and correction of curvature of the cross-sectional configuration of said beam of ions, said beam correcting means comprising:

six electrode means disposed in generally hexagonal configuration about said beam of ions and positioned in a plane at substantially said location at which said area is of minimum value and,

circuit means coupled to each said electrode means for applying electrical signals, each of a predetermined value, to said electrode means to establish an electrostatic field about said beam of ions to thereby effect rotation of and correction of curvature of said beam configuration at said location at which said area is of minimum value.

2. An apparatus as defined in claim 1 wherein said six electrode means are positioned symmetrically about said beam of ions.

3. An apparatus as defined in claim 2 wherein each said electrode means is an elongated member having a longitudinal axis extending in a direction generally parallel to a longitudinal axis of said beam of ions.

4. An apparatus as defined in claim 1 including means for accelerating ions out of said ionization chamber, a voltage supply source having an output circuit means for developing an accelerating signal and including means for varying the value of said accelerating signal; second circuit means coupling said output circuit means to said ion accelerating means for applying a said signal to said accelerating means; and, said circuit means coupled to said electrode means including means coupled to said output circuit means in a manner so that said signals applied to said electrode means vary in value in accordance with the value of said accelerating signal.

5. In a mass spectrometer including an ionization chamber for ionizing a sample to be analyzed, said ionization chamber being coupled to an elongated housing member having a through passageway for the passage of a beam of ions, a magnetic analyzer disposed to apply a magnetic field to said beam to analyze said ions, detection means coupled to said housing and disposed to detect said ions after analysis, and beam correcting means comprising:

a first set of six electrode means disposed in generally hexagonal configuration about said beam of ions and disposed in close proximity to one end of said magnetic analyzer;

first circuit means coupled to each said electrode means for applying electrical signals, each of a predetermined value,

to said electrode means to establish an electrostatic field about said beam of ions to thereby introduce curvature into said beam configuration before the beam enters said magnetic analyzer;

a second set of six electrode means disposed in generally hexagonal configuration about said beam of ions at the other end of said magnetic analyzer; and,

second circuit means coupled to each of said second set of electrode means for applying electrical signals, each of a predetermined value, to said second set of electrode means to establish an electrostatic field about said beam of ions to thereby remove curvature from said beam configuration after the beam exits from said magnetic analyzer.

6. An apparatus as defined in claim wherein the electrodes of each of said sets of six electrode means are positioned symmetrically about said beam of ions.

7. An apparatus as defined in claim 6 wherein each said electrode means is an elongated member having a longitudinal axis extending in a direction generally parallel to a longitudinal axis of said beam of ions.

8. An apparatus as defined in claim 5 including means for accelerating ions out of said ionization chamber; a voltage supply source having an output circuit means for developing an accelerating signal and including means for varying the value of said accelerating signal; third circuit means coupling said output circuit means to said ion accelerating means for applying a said signal to said accelerating means; and, said first and second circuit means coupled to said output circuit means in a manner so that said signals which are applied to said electrode means vary in value in accordance with the value of said accelerating signal.

ill

9. A method of improving the resolution of a mass spectrometer including an ionization chamber assembly having an accelerating electrode positioned therein and being coupled to an elongated housing member having a passageway extending therethrough, a magnetic analyzer, a detection means, and a beam correcting means comprising the steps of:

introducing a sample to be analyzed into said ionization chamber assembly;

ionizing a said sample to thereby form ions;

applying an electrical signal to said accelerating electrode to accelerate substantially all of said ions out of said ionization chamber and into said passageway;

focusing said ions into a beam;

applying an electrical signal to said beam correcting means to thereby develop a field about said beam;

applying said field to said beam of ions to introduce curvature into the cross-sectional configuration of the beam;

applying an electrical signal to a said magnetic analyzer to thereby establish a magnetic field;

analysing said ions by deflecting with said magnetic field at least a portion of said ions in said beam; and,

detecting said beam, after analysis, by said detecting means.

10. A method of improving the sensitivity of a mass spectrometer as defined in claim 9 including the further steps of:

applying an electrical signal to another beam correcting means to thereby develop a second field about said beam at a second point along said beam; and,

applying said second field to said beam of ions to remove curvature from the cross-sectional configuration of the beam. 

1. In a mass spectrometer including an ionization chamber for ionizing a sample to be analyzed, said ionization chamber being coupled to an elongated housing member having a through passageway for the passage of a beam of ions, said beam of ions having a cross-sectional configuration which varies in area along the length of said beam and having at least one location at which said area is of a minimum value, a magnetic analyzer disposed to apply to a magnetic field to said beam to analyze said ions, detection means coupled to said housing and disposed to detect said ions after analysis, and beam correcting means for effecting rotation of and correction of curvature of the cross-sectional configuration of said beam of ions, said beam correcting means comprising: six electrode means disposed in generally hexagonal configuration about said beam of ions and positioned in a plane at substantially said location at which said area is of minimum value and, circuit means coupled to each said electrode means for applying electrical signals, each of a predetermined value, to said electrode means to establish an electrostatic field about said beam of ions to thereby effect rotation of and correction of curvature of said beam configuration at said location at which said area is of minimum value.
 2. An apparatus as defined in claim 1 wherein said six electrode means are positioned symmetrically about said beam of ions.
 3. An apparatus as defined in claim 2 wherein each said electrode means is an elongated member having a longitudinal axis extending in a direction generally parallel to a longitudinal axis of said beam of ions.
 4. An apparatus as defined in claim 1 including means for accelerating ions out of said ionization chamber, a voltage supply source having an output circuit means for developing an accelerating signal and including means for varying the value of said accelerating signal; second circuit means coupling said output circuit means to said ion accelerating means for applying a said signal to said accelerating means; and, said circuit means coupled to said electrode means including means coupled to said output circuit means in a manner so that said signals applied to said electrode means vary in value in accordance with the value of said accelerating signal.
 5. In a mass spectrometer including an ionization chamber for ionizing a sample to be analyzed, said ionization chamber being coupled to an elongated housing member having a through passageway for the passage of a beam of ions, a magnetic analyzer disposed to apply a magnetic field to said beam to analyze said ions, detection means coupled to said housing and disposed to detect said ions after analysis, and beam correcting means comprising: a first set of six electrode means disposed in generally hexagonal configuration about said beam of ions and disposed in close proximity to one end of said magnetic analyzer; first circuit means coupled to each said electrode means for applying electrical signals, each of a predetermined value, to said electrode means to establish an electrostatic field about said beam of ions to thereby introduce curvature into said beam configuration before the beam enters said magnetic analyzer; a second set of six electrode means disposed in generally hexagonal configuration about said beam of ions at the other end of said magnetic analyzer; and, second circuit means coupled to each of said second set of electrode means for applying electrical signals, each of a predetermined value, to said second set of electrode means to establish an electrostatic field about said beam of ions to thereby remove curvature from said beam configuration after the beam exits from said magnetic analyzer.
 6. An apparatus as defined in claim 5 wherein the electrodes of each of said sets of six electrode means are positioned symmetrically about said beam of ions.
 7. An apparatus as defined in claim 6 wherein each said electrode means is an elongated member having a longitUdinal axis extending in a direction generally parallel to a longitudinal axis of said beam of ions.
 8. An apparatus as defined in claim 5 including means for accelerating ions out of said ionization chamber; a voltage supply source having an output circuit means for developing an accelerating signal and including means for varying the value of said accelerating signal; third circuit means coupling said output circuit means to said ion accelerating means for applying a said signal to said accelerating means; and, said first and second circuit means coupled to said output circuit means in a manner so that said signals which are applied to said electrode means vary in value in accordance with the value of said accelerating signal.
 9. A method of improving the resolution of a mass spectrometer including an ionization chamber assembly having an accelerating electrode positioned therein and being coupled to an elongated housing member having a passageway extending therethrough, a magnetic analyzer, a detection means, and a beam correcting means comprising the steps of: introducing a sample to be analyzed into said ionization chamber assembly; ionizing a said sample to thereby form ions; applying an electrical signal to said accelerating electrode to accelerate substantially all of said ions out of said ionization chamber and into said passageway; focusing said ions into a beam; applying an electrical signal to said beam correcting means to thereby develop a field about said beam; applying said field to said beam of ions to introduce curvature into the cross-sectional configuration of the beam; applying an electrical signal to a said magnetic analyzer to thereby establish a magnetic field; analysing said ions by deflecting with said magnetic field at least a portion of said ions in said beam; and, detecting said beam, after analysis, by said detecting means.
 10. A method of improving the sensitivity of a mass spectrometer as defined in claim 9 including the further steps of: applying an electrical signal to another beam correcting means to thereby develop a second field about said beam at a second point along said beam; and, applying said second field to said beam of ions to remove curvature from the cross-sectional configuration of the beam. 